Sleep apnea is a common disorder with significant morbidity that affects at least 4% of middle-aged males and 2% of middle-aged females. Obesity is thought to be the most important risk factor for obstructive sleep apnea yet we do not understand how obesity predisposes to sleep apnea. Not all obese subjects have sleep apnea. The focus of this proposal is directed towards understanding the relationship between obesity and obstructive sleep apnea by examining tissue properties and the biologic behavior of the tongue. In particular we will examine tongue fat with high definition volumetric spin echo MRI, Dixon imaging for fat and water and MR spectroscopy and the metabolic function of the tongue with PET imaging in patients with sleep apnea and weight matched controls before and after weight loss. Weight loss will be achieved medically in half the subjects and surgically in half of the subjects. It is critical to understand exactly how obesity affects upper airway function in order for us to determine better treatment options and preventive strategies for patients with sleep apnea. This proposal is based on the overall hypotheses that patients with sleep apnea will have more fat in the tongue and increased metabolic activity of the tongue as compared to weight matched controls. Our specific aims are: 1) To compare the tissue properties and metabolic function of the tongue and other upper airway soft tissue structures in apneics and weight-matched controls without apnea;and 2) to determine the differences in the tissue properties and metabolic function of the these structures after weight loss. Our resources, which include advanced static and dynamic MR imaging techniques, novel volumetric computer graphics image analysis paradigms, a world renown PET imaging center and expertise in sleep apnea biostatistics, polysomnography, imaging the upper airway, weight loss studies, Pcrit and tongue force measurements will allow us to achieve our specific aims. PUBLIC HEALTH RELEVANCE: Obesity is reaching epidemic proportions in this country. Obesity is the biggest risk factor for obstructive sleep apnea, a condition characterized by snoring, daytime sleepiness and airway closure during sleep. This grant is designed to understand the relationship between obesity and sleep apnea so that we can determine optimal treatment strategies for this disorder.